1. Field of the Invention
The present invention relates to a novel phosphonamidothionate derivative and a process for the preparation thereof. The present invention also relates to a pesticidal composition containing the novel compound and a method for combatting insect pests. More particularly, the present invention is concerned with a novel phosphonamidothionate derivative represented by the formula ##STR2## wherein R.sup.1 and R.sup.2 each independently represent a straight-chain alkyl group having 1 to 4 carbon atoms or a branched alkyl group having 3 or 4 carbon atoms and R.sup.3 represents a phenyl group unsubstituted or substituted with a chlorine atom, a methyl group, a nitro group, a methylthio group or a nitrile group, an alkyl group having 1 to 4 carbon atoms or a 5-methyl-2-isoxazolyl group. The novel compound is characterized by a high pesticidal activity which lasts for a long period of time after application. The present invention is also concerned with a unique process for preparing the phosphonamidothionate derivative, in which the direct phosphorylation of a carbamate compound is involed, a pesticidal composition comprising as an active ingredient the above-mentioned novel compound and a method for combatting sanitary insect pests, or agricultural and horticultural insect pests by using the compound.
2. Discussion of Related Art
Various organophosphorus pesticides, carbamate pesticides and pyrethroid pesticides are used for combatting agricultural insect pests. However, none of the conventional pesticides have a long lasting effect after application. In general, if a pesticide is applied to farm land, the crops on the farm land are protected only for the period in which the pesticide remains active. This is because there are some insect pests on farm land which are not killed by the application of the pesticide, and these insect pests harm the crops when the pesticidal activity of the pesticide is lost. In addition, when the activity of the pesticide is lost, insect pests fly from the neighboring farm lands into the farm land and harm the crops thereon. Accordingly, for protecting crops by using a conventional pesticide in regions where insect damage frequently occurs, it is required to repeat the application of the pesticide at short intervals. This necessitates a considerable amount of labor, leading to great disadvantages.
U.S. Pat. No. 4,683,224 discloses the pesticidal activity of an N-formyl phosphonamidothionate which has such a chemical structure as is obtained by substituting, in the chemical structure of formula (I), a group of the formula --SR.sup.3 for the group of the formula --OR.sup.3, formamide for the carbamate moiety and a P=0 bond for the P=S bond. European Patent Application Laid-Open Specification No. 0 164 308 discloses the pesticidal activity of an N-formyldithiophosphonic acid amide which has such a chemical structure as is obtained by substituting, in the chemical structure of formula (I), a group of the formula --SR.sup.4, wherein R.sup.4 represents an alkyl group or an alkenyl group, for the group of the formula--OR.sup.3 and formamide for the carbamate moiety. U.S. Pat. No. 4,168,305 discloses the pesticidal activity of an S-alkyl-N-carbonyl-alkanedithiophosphonic acid ester amide which has such a chemical structure as is obtained by substituting, in the chemical structure of formula (I), a hydrogen atom for the alkyl group represented by R.sup.1 and a group of the formula --SR.sup.5, wherein R.sup.5 represents an alkyl group, for the group of the formula --OR.sup.3. However, these conventional compounds are not satisfactory with respect to pesticidal activity.
Further, there is known a compound which has such a chemical structure as is obtained by substituing, in the chemical structure of formula (I), a hydrogen atom for the alkyl group represented by R.sup.1 (see, for example, Zh. Obshch. Khim. Vol. 37, 2069 (1967) and Fiziol. Aktiv. Veshchestva 1969, No. 2, 37). However, this compound is not satisfactory with respect to pesticidal activity, as set forth in the Examples hereinbelow.